Digital cryptographic signatures, which may be herein referred to as digital signatures, may often be used in messaging systems to provide security features including authentication of the source of the message, message integrity, and non-repudiation of origin. In messaging systems where a message originating from a communication device passes through a server or another communication device, there may be situations in which the server may add to the message. For example, the server may add text or attachments. Some devices may wish to digitally sign the sent message. However, in order to do so, some conventional systems may provide incomplete authentication since the communication device may be signing a message that has been subsequently changed by the server to add the text or attachments. Other difficulties with existing systems may be appreciated in view of the detailed description below.
Like reference numerals are used throughout the figures to denote similar elements and features.